We have demonstrated that p-bromophenol does not cause either hepatic or renal toxicity even at very high doses in rats pretreated with phenobarbital and diethyl maleate to nontoxic reactive metabolites in vivo. Since p-bromophenol is converted to metabolites that covalently bind to protein, these results support the view that the reactive metabolites of p-bromophenol do not contribute to the toxicity of bromobenzene, even though they may contribute to covalently bound radioactive material.